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Indian I. Plant Phy,;ol., Vol. XXIX, No.4, pp. 397-404 (December, 1986)
LEAF WATER CONTENT, STOMATAL CONDUCTANCE AND PROLINE ACCUMULATION IN LEAVES OF POTATO (SOLANUM TUBERSOSUML.) IN RESPONSE TO WATER STRESS K. C. BANSAL AND SHANTHA NAGAR.AIAN
Central Potato R.esearch Institute, Simla
SUMMARY
To find out a physiological tool to serve as an index of drought
resistance, tbe response of potato to water stress was studied in ten geno­
types grown in earthenware pots. Water stress was imposed at tuber
initiation stage by witbbolding watering for a week.
Water saturation deficit in leaves was found to be significantly
correlated witb tuber weight (r=-0.889**) and tuber number
(r=-O,870·*) under stress conditions, whereas in non-stressed plants
water saturation deficit correlated with tuber weight (r=-O.793**) but
not with tuber number. Stomatal conductance negatively correlated with
tuber Weicht (r=-O.961**·) and with tuber number (r=-0.887··)
under stress conditions which suggests that yield is reduced by loss in
leaf water content rather tban stomatal closure. No significant correlation
existed between stomatal conductance and tuber weight or number in
non-stressed plants. Proline accumulation in leaves sbowed a significant
negative correlation with tuber weigbt (r=-0.792*) and tuber number
(r=-0.902*·) in stressed plants. In non stressed plants proline accumul-,
alion in leaves correlated negatively (r=-0.7S2·) with tuber number.
Tbe study indicated that stomatal conductance was a better parameter to
serve as an index for drought resistance than water saturation deficit
and proline content in leaves of potato.
INTRODUCTION
Stomatal behaviour which influences the water status of the plant tissues
during a period of water deficit is of importance in determining the growth
rate of plants during drought (May and Milthorpe 1962). O'Toole and Chang
(1978) who worked with rice felt that evalution of stomatal behaviour as an
indicator of drought stress is problematic. However. Shimshi and Ephrat
(1975) while working with II cultivars of spring wheat, suuested that porometer
method, used to measure stomatal resistance. would be useful in wheat breeding
•
~fh(1
398
K. C. BANSAl.; AND SHANTIIA NAGARAJAN
programmes. Adjei and Kirkham (1980) were also of similar opinion and felt
that total plant resistance was not as good an indicator of drought resistance as
was stomatal resistance. In potato, correlation existed between diffusive Jeaf
resistance and yield under stress but varied greatly from one season to the next
(Dwelle et al., 198 I). Levy (l983a) observed no correlation between stomatal
conductance and yield as the cultivars with differing values of stomatal conduc­
tance produced similar tuber yields under stress. It is, therefore, not certain
whether stomatal conductance could be used as tool for screening for drought
resistance in potato. Keeping in view the above results, the present investi­
gation was carried out (I) to determine physiological responses to drought and
(2) to find out a physiological tool to serve as an index of drought resistance.
MATERIALS AND METHODS
Plants were raised in a green house through eye plugs in 25 em diameter
earthenware pots containing soil rich in farm yard manure· Ten potato geno­
types viz. Kufri Jyoti. Kufri Chandramukhi.Kufri Kundan, Kufri Muthu.
Kufri Dewa, Kufri Sindhuri, Up-to-Date, ON 1645. G 2524 and Phulwa were
planted as single plant per pot. Total pots in each genotype were divided into
two groups of plants. 55 days after planting, stress was imposed by withholding
watering for a week, while the plants of the other group were watered daily to
act as control. The stressed plants were later rewatered and allowed to grow
at a normal water supply until maturity. The mean maximum, minimum
temperatures and relative humidity during the growth season were 22.6°, 16.4°C
and 74.2 per cent, respectively. At the end of stress period, the following
observations were recorded on stressed and control plants.
Leaf water status : To know the leaf water status of plants, per cent water
saturation deficit (WSD) in 4th leaf counting from top was determined. as des­
cribed by Barrs (1968).
Stomatal conductance: Stomatal conductance on the lower epidermis of
5th leaf from top was determined by stomatal infiltration technique (Fuehring
et al., 1966) and the values were expressed as solution number ranging from
1 to 11.
Proline coment: Proline content in leaves was determined using 5th leaf
from top, following Bates et al. (1973) and expressed as mg per g fresh weight.
Tuber weight Qnd number: At maturity, haulms were cut and after a
week of cutting the haulms, tubers were counted and weighed. The data were
analysed statistically.
i.;;
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399
RESPONSE OF POTATO GENOTYPES TO WATBR STRESS
RESULTS AND DISCUSSION
Significant increase in WSD was observed due to stress in aU the geno­
types (Table I) thereby indicating a decrease in leaf water content. No signifi­
cant differences in WSD within genotypes were noticed in the plants watered
regularly whereas in stressed genotypes, significant differences occured. Phulwa
a known drought resistant (hardy) cultivar (Pusbkarnath, 1969) and G 2524 had
the lowest values of WSD compared to other genotypes.
Stomatal conductance decreased significantly due to stress in all the
genotypes (Table I), and on the final day of stress, Phulwa and G 2524 had the
lowest &tomatal conductance. These low values of stomatal conductance could
have been responsible for leaf turgor maintenance under stress conditions in
both the genotypes. Unlike WSD, significant differences among genotypes were
Table I: Effect of water stress on water saturation deficit (WSD) , stomatal
conductance and proline content in leaves of ten potato genotypes.
The values are the averages of three to five replications.
Stomatal Conductance
(solution number)
WSD
Genotype
(%)
--------Stress
Control
".
"
f
,/
Control
Stress
-1
(mg. gfr. wt)
--------­
Control
Stress
Kufri Jyoti
2.29
4257
8.0
4.0
0.019
3.758
Kufd Chandra­
mukhi
0.15
41.71
7.8
4.8
0.017
3.534
Kufri Kundan
0.00
48.86
9.8
40
0.024
4.295
Kufri Muthu
0.22
3HI 9
9.0
3.6
0.024
2.543
Kufd Dewa
1.55
34.14
5.6
3.5
0.030
2213
Kufri Sindhuri
1.01
45.67
6.8
4.0
0.027
2.705
Up-to· date
0.21
35.50
8.0
3.8
0.023
2.495
ON 1645
0.97
30.11
7.6
3.3
0.033
2.122
G 2S24
0.54
26.89
5.1
2·0
0.026
1.748
Phulwa
2.37
25.16
6.1
2.2
0.040
1.747
L. S. D. lO.OS)
r
-------­
Proline
3.93
1.2
0.978
r ...
-~~.
I
400
K. C. BANSAL AND SHANTIIA NAGARAJAN
recorded in stomatal conductance in well watered plants which indicates diffe­
rential water uptake behaviour of roots in different genotypes. In genotypes
like Phulwa, G 2524 and Kufd Dewa, stomatal conductance was significantly
low.compared to other genotypes grown under regular watering which suggested
the inability of these genotypes to take up water from the soil. In these geno­
types, turgor is, therefor, maintained by stomatal closure. Depletion of more
soil water by a susceptible cultivar (King Edward) than a resistant cultivar
(Majestic) has been suggested to be related with stomatal behaviour (Aageeb
1968).
Free proline accumulation has been observed in leaf tissue in response
to water stress (Chen et 01., 1964; Levy 1983b; Singh et 01., 1972). We also
noticed accumulation of free proline in leaves due to stress in all the genotypes;
.the accumulation being the least in Phulwa and G 2524 (Table I), The low
proline content as a result of water IttesS, in a resistant cultivar, therefore
suggests a negative correlation between the proline content in leaves and the
relative tolerance to stress, as shown by Levy (l983b).
Table II : Effect of water stress on tuber fresh weight and tuber number in ten
potato genotypes. The values are the averages of twelve replications.
Genotype
Tuber Fr. wt.
(II/plant)
----------
Tuber number
(No./plant)
Control
Stress
Kufri Jyoti
30.00
19.38
2.1
1.6
Kufri Chandramukhi
33.67
20.80
2.4
1.8
Kufri Kundan
33.64
27.92
2.1
1.8
Kufri Muthu
30.56
31.36
:Z.O
2.1
Kufri Dewa
3t.25
35.00
2.5
2.8
7.67
0.75
1.6
OS
Up-to-date
33.33
29.33
3.0
2.8
ON 1645
30.25
34.42
2.7
3.3
G2524
33.33
52.0&
3.1
4.3
Phulwa
29.17
42.92
4.3
5.8
Kufri Sind uri
L. S. D. (0.05)
8.84
Control
Stress
1.1
~
RESPONSE OF POTATO GENOlYPES TO WATER STRESS
401
Tuber weight decreased under stress in Kufri Jyoti and Kufri Chandra­
mukhi to the extent. of 35% and 38%, respectively, (Table II). But in case of
resistant cultivar Phulwa and G 2524 the tuber weight increased in response to
stress which is in agreement with the results obtained by Wilcox and Ashley
(1982). No significant decrease or increase in tuber weight was observed in other
genotypes. Under stress conditions, Phulwa and G 2524 produced significantly
higher tuber weight than other genotypes. This could be due to low stomatal
conductance as a result of delayed stomatal response to' increased leaf water
content after rewatering (Ackerson it al., 1977). Low stomatal conductance
might have resulted in better leaf expansion rate in Phulwa and G 2524 than
other genotypes, so that more leaf area was available for photosynthesis to occur
and hence more tuber weight produced in the two genotypes. Wolfe et al.,
(1982) suggested that the effect of water stress on dry matter production in
potato, was largely a function of effects on leaf area duration.
WSD was found to be significantly and negatively correlated with tuber
fresh weight and tuber number (r= -0.889, P=O.Ol and r=-o.870, P=O.Ol. res­
pectively) under stress conditions (Table III) whereas in non-stressed plants
WSD correlated with tuber fresh weight (r=-0.793, P=O.OS) and no significant
correlation was observed with tuber number (Table IV).
Table III : Simple linear correlation coefficient between water saturation deficit
(WSD), stomatal conductance, proline content, tuber fresh weight
and tuber number in ten potato genotypes grown under stress
conditions.
WSD
WSD
.
Stomatal
. conductance
0.859··
Stomatal
conductance
Proline
content
Tuber fresb
weight
Tuber number
·(P.0.05), ··(P-O.Ol), ···(P=O.OOI).
,.
•
Proline
content
Tuber fresh
weight
Tuber Number
0.965···
-0.889··
-0.870*·
0.758·
-0.961···
-0.887··
-0.792·
-0.802··
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402
K. C. BANSAL AND"SHANrnA NAGARAJAN
Table IV : Simple linear correlation coefficients betwecn water saturation deticit
(WSD). stomatal conductance, proline contcnt, tuber fresh weight
and tuber number in ten potato genotypes grown under well watered
conditions.
-"
WSD
WSD
Stomatal
conductance
Proline
content
Tuber fresh
weight
Stomatal
conductance
-0.462 NS
1
Proline
content
0.316 NS
-0.497 NS
Tuber fresh
weight
Tuber number
-0.793*
-O.OO7NS
-0.130 NS
-0.612 NS
-0.384 NS
-0.752* NS
-0.266 NS
Tuber number
*(P=O.05).
NS = Non-Significant
Stomatal conductance had a highly significant negative correlation with
tuber fresh weight (r=-0.961, P=O.OOl) and a significant negative correlation
with tuber number (r=-o.887. P=O.Ol) under stress conditions, which suggestes
that yield is reduced by loss in leaf water content rather than stomatal closure
(Hsiao 1973). The negative correlation between stomatal conductance and tuber
fresh weight also reveals that leaf turgor is more important than photosynthe.sis
in determining tuber yield under stress. Wilcox and Ashley (1982) found no
significant differences in photosynthetic rate between stressed and control plants
of four potato cultivars but they did observe an increase or decrease in tuber yield
due to stress. No significant correlation existed between stomatal conductance
and tuber weight and number in well watered controls (Table IV). This could
be because in case of control plants, stomatal aperture remains open for most
of time and the flow of the water continues from the soil to the atmosphere
through the stomatal opening, whereas in stressed plants, stomata close and
conserve water to maintain the maximum possible leaf water content. The
extent to which the stomata close i~ response to stress is a varietal characteristic
which is tinally reflected in less or more tuber yield under stress conditions.
Proline accumulation in . leaves showed a significant negative correlation
with tuber fresh weight (r=-0.792, P=0.05) and tuber number (r=-0.802,
RESPONSE OF POTATO GBNOTYPES TO W ATIlR STRESS
403
P=O.OI) in stressed plants (Table III). Levy (1983b) pointed out the possible
association of proline accumulation in tuber tissue with relative drought
susceptibility. Similar is the case with proline accumulation in leaves in res­
ponse to stress and drought susceptibility as per the results obtained in the
present study. This is in agreement with the results obtained by Hanson et 01.
(1979) who showed a highly significant positive correlation between proline
accumulation and drought injury in barley.
The data suggest that stomatal conductance is a better parameter to serve
as an index for drought tolerance thall WSD and proline content in the leaves
as it shows highest correlation with tuber yield among the three parameters and
is related directly for the maintenance of turgor which in turn is responsible for
better performance of potato under water stress conditions.
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--,'
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,,
404
K. 'c. BANSAL AND SHANTHA NAGARAJAN '
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